Conventionally, research and practical applications are carried forward for a device for making an alert regarding another vehicle that is likely to cross with a self-vehicle, when the self-vehicle starts to reverse after moving forward into a parked state. This type of device detects another vehicle that is approaching with a millimeter-wave radar, and when there is another vehicle moving in a predetermined alert area set based on the self-vehicle, the device performs control such as emitting an alert sound.
Incidentally, when parking a vehicle, the vehicle is not necessarily parked at a right angle with respect to the original driving lane (a regular driving road, including parts other than the inside of the parking frame at a parking lot where plural vehicles can be parked). It is assumed that the vehicle may be parked at a slanted angle or at a near-parallel angle with respect to the driving lane. Therefore, if the above alert area is set in a uniform manner, depending on the angle with respect to the driving lane, the alert area may deviate from the area that is supposed to be alerted.
There is known a cross traffic alert device considering the above problem (see, for example, patent document 1). In this device, by sampling the yaw rate and the steering angle until the parked state is reached, the parking angle that is the angle of the parked vehicle with respect to the driving lane is calculated, and the parking angle is stored in a non-volatile memory. When the parking state ends, and the vehicle starts to reverse, the angle range of the alert area is set based on the parking angle (FIGS. 2, 4, and 5).